Contemporaneous training of multiple individuals separated by substantial geographical distances can be provided using a distributed system of simulators connected by a network, such as the Internet or a dedicated long-haul DMO network. In such a distributed system, each simulator is supported by a local computer system that has stored therein scene data that defines the position and appearance of all the objects in the virtual environment, and from that scene data, the simulator computer system renders and displays a view of the virtual environment as it is influenced by the various individuals in the simulators.
The delays in the communications over the network produce some latency between remotely spaced simulator systems, in that data transmitted as electrical signals over the network that controls the position of objects in the virtual world arrives at different simulators at slightly different times. This latency can result in the versions of the scene data stored in memory at each simulator being divergent, sometimes with radically different effects in terms of the consequences of movement, e.g., where a plane passes a building safely in one version of the virtual world, and in another version the same plane crashes into the building. Where latency is, for example, 220 milliseconds, the time period corresponds to 90 feet of error at 250 knots. It can be understood easily that an error of 90 feet may be significant. The lateral and vertical movement is also delayed.
To try to overcome some problems of latency, systems have been developed in which each simulation station computer has a physics engine that provides for more realistic interaction of objects in the immersive environment according to physics rules. One such system is the system disclosed in International Patent application PCT/US2006/045569 filed Nov. 28, 2006 entitled DISTRIBUTED PHYSICS BASED TRAINING SYSTEM AND METHODS and published on May 31, 2007 as application no. WO/2007/062260, and also published on Apr. 16, 2009 as U.S. published application US2009/0099824 A1, both herein incorporated by reference. In that system, signals corresponding to physics data is sent over the network and received at remote simulators, where the data is used to control movement of the relevant objects in a local physics engine at the local simulator computer system. The physics based movements of objects are reflected in the scene data stored electronically at the local simulator system and displayed to the user.
Notwithstanding the advantages of a physics-based environment generating system for supporting a shared virtual environment over a distributed system of simulators, there are still some scenarios where latency presents a problem of divergence of versions in two simulator stations. One such situation is encountered where two virtual aircraft are each controlled by a human trainee, and at least one of the trainees is trying to establish a spatial relationship with the other aircraft, such as in a dogfight when trying to establish a line of fire on an enemy aircraft, a tactic requiring formation flight in close proximity to a companion aircraft, or in an in-flight refueling operation where a receiver aircraft has to fly in close formation with a tanker from which it derives fuel.
In such scenarios, one pilot may move in one direction while the other pilot moves in a different direction, and latency between the two sources of input may result in a compound of error that produces a jittery interaction in one or both simulators that is unrealistic in appearance and undesirable from a training standpoint.
Compensation using traditional prediction techniques results in overshoot and oscillation of the remote vehicle position from its true position. Dead reckoning in accordance with the DIS protocol can result in sudden jumping to the remote aircraft position, requiring additional filtering and adding to the error, or in the case of tight dead reckoning tolerance settings a flood of high rate packets on the network consuming unacceptable bandwidth.
Position and velocity oscillations that occur between the tanker, receiver and boom operator when the trainers are located at remote sites, even with traditional smoothing and prediction techniques, make it objectionable to pilots performing the refueling tasks, thereby rendering training ineffective. Refueling must therefore be performed using operational aircraft, resulting in additional cost and risk.
Similar problems of velocity or position oscillations occur in other close-range maneuvering operations that make the training and simulation less effective.